The long-term goals of this project are to understand the function and regulation of protein phosphorylation in control of cell growth, proliferation and differentiation, and the molecular mechanism of growth factor-induced signal transduction. Cell growth is the integrated outcome of cellular response to the extracellular environment, including nutrients, growth factors, and stress conditions. Cell mass accumulation is mainly reflected by the rate of protein synthesis. Tuberous sclerosis (TSC) is an autosomal dominant genetic disorder occurring in 1/6000 of the population. TSC is characterized by the development of harmatomas in a wide range of human tissues. Mutations in either the TSCI or TSC2 tumor suppressor gene are responsible for TSC. Recent genetic studies indicate that the TSC genes are involved in cell growth regulation. However, the precise molecular functions of TSC1 and TSC2 gene products in cell growth regulation are unknown. The major goals of this proposal are to test the model that TSC1/TSC2 play a central role of receiving both extracellular and intracellular signals to regulate cell growth. TSC1/TSC2 functions in vivo to regulation protein translation by inhibiting the phosphorylation and activity of the p70 ribosomal S6 kinase. Biochemical and cell biological approaches will be used to investigate the regulation of TSC2 by phosphorylation in response to growth factor stimulation, nutrient and ATP depletion, and cellular stress conditions.